The sealing material obtained according to the process of the present invention has a number of advantages: excellent waterproofness without incorporation of any waterproofing filler; low temperature sensitivity, i.e. no tendency to become badly soft and flabby even in summer; little change in stiffness depending on compression ratio; and easy handling with no tack and without contaminating the substrates to be applied. The manufacturing method is also easy; the lipophilic filler, if desired, can be incorporated in the product simply by formulating it in the foaming compound. This eliminates the need for troublesome after-treatments required in conventional processes, such as subsequent impregnation of waterproofing agents, or subsequent lamination or formation of a film on the product surface. Any desired shape can be easily obtained by cutting the foamed product. These are excellent features of the present invention not expected in conventional processes.
The polyurethane foam has been changed from the polyester type, which was the mainstream at its earlier stage of development, to the polyether type. Particularly, in terms of higher moisture absorption, antistatic property and higher productivity through increased rate of reaction, desired in its application to cushioning materials, such as mattresses, addition polymers, such as polypropylene oxide and polypropylenethylene oxide, are commonly used in recent years as the base material. This shows a tendency toward higher hydrophilicity, the reverse of waterproofing characteristics.
Such hydrophilic polyurethane foams, if not treated otherwise, cannot prevent water leaks (1) even in the compressed state, (2) even if the air permeability is reduced near zero, or (3) even at low water pressures.
In order to use these hydrophilic polyurethane foams as a waterproofing material, many attempts have been made. The only way heretofore available to render them waterproof is to impregnate a waterproofing agent into the foamed products previously prepared in an aftertreatment. As typical examples of this process and waterproofing agents used, may be mentioned the following.
Polyurethane foams in which a waterproofing agent is used, such as asphalt, polybutene and low molecular-weight butyl rubber, are well known.
These polyurethane foam sealing materials are produced, for example, by the following methods:
(1) An open-cell polyurethane foam is cut to an appropriate size, impregnated with a solution of asphalt in a volatile solvent, and dried.
(2) Instead of the asphalt solution used above, an aqueous suspension of asphalt is employed.
These methods include the troublesome impregnation and drying steps, reducing the productivity. In addition, uniform and thorough impregnation of asphalt into the material cannot be achieved when the cell size and air permeability are not sufficiently large or when the thickness of the foam material is large.
Method (1) requires a large amount of volatile solvent to dissolve asphalt. This may cause air pollution problems, various harms to human bodies, and fire hazards. Other difficulties involved in this method are: the long time required for drying; low productivity; tacky feeling of the product and contamination of the substrates to which the product is applied; and high temperature sensitivity of the product, i.e. reduced stiffness in summer and lower recovery speed after compression.
In method (2), the disadvantages of method (1) caused by the use of a volatile solvent have been overcome. However, this method suffers from the following difficulties: a long drying time and low productivity; and the use of an emulsifier to disperse asphalt in water, which will remain in the product after drying and lower its waterproofness when in contact with water.
Other methods for producing polyurethane foams incorporating a bituminous substance, such as asphalt and petroleum pitch, are also known: for sealing applications, (1) a liquid mixture comprising a polyester polyol and/or a polyether polyol, an isocyanate, asphalt and a blowing agent, etc., is foamed-in-place in joints (Japanese Patent Publication No. 1672, 1965), (2) a mixture comprising a polyester polyol or polyether polyol, a bituminous substance, an isocyanate and a blowing agent, etc., is poured in a mold, wherein a sheet or film is placed on the surface before foaming begins to form an integral waterproofing skin layer (Japanese Patent Publication No. 1673, 1965); and (3) a first component comprising a polyester polyol or polyether polyol, a bituminous substance, a volatile organic solvent, a surfactant etc., and a second component comprising an organic polyisocyanate are mixed and foamed-in-place (Japanese Patent Publication No. 17598, 1968).
All these processes are intended merely to fill cavities with the polyurethane foaming materials or to achieve waterproofness by utilizing the skin layer.
As examples of polyurethane foam materials containing a bituminous substance intended for applications other than as sealing materials, may be mentioned: (4) a method of manufacturing building construction members to which a foaming material admixed with a softening agent, such as animal, vegetable or mineral oil, is sprayed in place (Japanese Patent Publication No. 21133, 1964); and (5) heat insulating materials with improved weather resistance incorporating petroleum pitch (Japanese Patent Publication No. 34117, 1971).
Furthermore, British Pat. No. 848,766 discloses, as an elastomer, polyurethane foams incorporating a bituminous substance, such as asphalt and petroleum pitch. However, these polyurethane foams are either closed-cell foams, or open-cell foams in which a non-foaming polyurethane elastomer is coated on the surface or a skin layer is formed by melting to form a waterproofing outer layer. The latter open-cell type structure requires after-treatments and its waterproofness will be lost when the outer protective layeer is broken.
The present invention is intended to offer a polyurethane foam sealing material free from the disadvantages of conventional ones mentioned above.